This invention relates generally to transmissions and, more particularly, to a speed change operating device suitable for use in continuously variable speed transmissions mounted on vehicles. More specifically, this invention relates to a transmission in which a plurality of operating devices are operated by one motor.
The applicant of the present invention has recently proposed a continuously variable speed transmission based on the combination of a belt drive continuously variable speed transmission (CVT), a high/low speed mode changeover mechanism and a forward/reverse rotation changeover mechanism, which transmission is disclosed in Japanese Laid-Open Official Gazette for Patent Application No. 63-158353.
The high/low speed mode changeover mechanism of this transmission has two frictional engagement components, i.e., a high clutch and a low-coast and reverse brake, and a low one-way clutch. In a low-speed mode, the low one-way clutch or the low-coast and reverse brake are operated to make the planetary gear function as a simple reduction mechanism, and the torque transmitted from the belt drive continuously variable speed transmission is output through this reduction mechanism. In a high speed mode, the high clutch is operated to directly input the torque from the input shaft to a predetermined element of the planetary gear through a transfer device, and the torque from the belt drive continuously variable speed transmission and the torque from the transfer device are combined at the planetary gear before being output.
In this continuously variable speed transmission, the speed of the belt drive continuously variable speed transmission is changed by means of an electric motor and a ball screw mechanism, while the operation of the forward/reverse rotation changeover mechanism for changing over the forward clutch and the reverse brake and the operation of the high/low speed mode changeover mechanism for changing over the high clutch and the low-coast and reverse brake are effected with hydraulic actuators.
This continuously variable speed transmission requires an oil pump having a comparatively large capacity because the forward/reverse rotation changeover mechanism and the high/low speed mode changeover mechanism are actuated by the hydraulic actuators for the changeover operations. In particular, in the forward/reverse rotation changeover mechanism, a changeover N.fwdarw.D (neutral.fwdarw.range D) and a changeover N.fwdarw.R (neutral.fwdarw.reverse range) are effected when the vehicle is stopped, and it is therefore necessary to set the discharge pressure and the discharge rate of the oil pump to substantially high levels in order to obtain a hydraulic pressure high enough to maintain the necessary engagement pressure and engagement time of the forward clutch or the reverse brake during idling rotation of the engine. There is therefore a consideration risk of oil leaks. Also, the oil pump loss may become excessively large, which is undesirable in terms of efficiency.
The applicant of the present invention has also proposed a continuously variable speed transmission in which the forward/reverse rotation changeover mechanism and the high/low speed mode changeover mechanism are also operated by mechanical actuators consisting of electric motors and ball screw mechanisms (Japanese Patent Application No.63-291634).
This continuously variable speed transmission can be designed to avoid the above-mentioned problems due to hydraulic pressure but entails the problem of the large size and weight of the electric motors and drivers available based on the present technology. In particular, the provision of three motors and corresponding drivers for one continuously variable speed transmission increases the total size of the transmission and entails difficulty in layout.